Churning cream involves agitating it at a suitable temperature to cause fat globules to adhere to each other and separate from the buttermilk. Successful churning depends on factors like cream temperature, fat content, churn speed and design. Theories propose that churning either causes a phase reversal from a water-in-oil emulsion to an oil-in-water emulsion, involves foam formation concentrating fat globules, or breaks up fat globule clusters allowing them to adhere into larger particles and emerge as butter.

1. CHURNING OF BUTTER-DEFINITION-THEORY
OF CHURNING-FACTORS INFLUENCING
CHURNABILITY OF CREAM

2. DEFINITION
• Agitation of cream at a suitable temperature
until the fat globules adhere forming larger
mass and until a relatively complete separation
of fat and serum occurs.
• The purpose of churning is to destroy the 5-10 nm thick
fat globule membrane
• Butter oil emerges from porous parts of membrane and
fat agglomeration takes place.
• For Agglomeration of fat globule into butter granules to
take place, its necessary that part of fat in crystalline
form.

3. Contd….
Agglomeration is difficult at too low temperature
when the proportion of liquid fat is too low
• And also difficult at too high temperature when all
the fat is in liquid form.
• So, Higher the fat content – lower should be the
temp.
• During churning the fat in water emulsion changes to
water in fat emulsion

4. Factors influencing churnability
 Chemical composition of fat
 Size of fat globules
 Viscosity of cream
 Temperature of cream
at churning
 Fat % of cream
 Acidity of cream
 Load of churn
 Nature of agitation
 Speed of churn

5. Design of butter churn
• Cylindrical wooden drum rotating around
horizontal axis
• Diameter- 2m & 2.5m long
• Cream 45% of its volume.
• Battens inside of churn help in formation of
foam & butter granules.
• Speed -20rpm
• Time -45 minutes
• Churning temperature : Winter --- 10-13°C;
Summer--- 7-9°C

6. • RPM for efficient churning varies with diameter.
• Large churns have small speed than smaller churns.
• High speed centrifugal force will exceed gravitational
force &cream will stick to periphery & rotate with drum.
• mw²R <m. g.
n=rpm
• (2∏n)² R < g
R = radius
• n < √(g/R)*1/2∏ ≈1/2√R
m=mass

7. Butter churn

8. Cylindrical butter churn

9. Conical butter churn

10. THEORIES OF CHURNING
• FISHER AND HOOKER ‘S PHASE REVERSAL
THEORY
 Churning is a process of phase reversal
 Changing oil in water type of emulsion to
• Water in oil type of emulsion
 Agitation in cream
 Causes coalescence and clumping of fat
globules
The ratio of surface area to volume of fat --
so small
 No longer contains all the buttermilk in
stable form
 Fat in water emulsion breaks

11. RAHN’S FOAM THEORY
• cream contains a foam producing substance which
gets solidified gradually when cream (or milk) is
agitated.
• During churning:
first foam is produced
fat globule tend to concetrate on the foam bubble
clumping of fat globule takes place
thus the foam producing assumes a solid character
and the foam collapse.
Then the fat globules is tend to form coalesce and
butter is formed

12. Contd…
• Based on his findings Rahn conclude that:
Air was necessary for normal churning of butter.
In the absence of air did not result in churning of
cream.
Overloading of churn resulting in increased
churning time.
But this theory is criticized because of the fact that
foam formation i.e. presence of air, is not required in
some of the continuous butter making processes

13. KING’S MODERN THOERY
• In cooled cream, fat is present as clusters of
fat globules.
• Within each globule it is present partly as solid
and partly liquid.
 Churning breaks the clusters and causes
foam formation
 fat globules become concentrated to air bubble
in the foam
thus are brought into close contact of each
other.
The globules then adhere together to form
larger and larger particles. Eventually these
particles become visible as butter grains.

14. Contd…
The butter grains causes the globules to move
over one another.
• Finally the butter is obtained